1. Field of the Invention
The invention relates in general to a calibration mechanism, and more particularly to a calibration mechanism of a scanning device thereof.
2. Description of the Related Art
The scanner is mainly used for scanning a document or a photo, and then transforming the image into an electronic file for the convenience of storage, transmission and editing. The automatic document feeder (ADF) scanner, a scanner used for scanning a double-sided document or image, is both time-saving and convenient to the user.
Referring to FIG. 1A, an ADF scanner is shown. The ADF scanner 100 includes a body 101 and an ADF 103. The body 101 includes a bottom chassis 107 and a calibration sheet 108. The ADF 103 includes a top chassis 105. The top chassis 105 and the bottom chassis 107 are used for scanning different sides of a document to obtain the image data from different sides of the document.
When the scanner 100 is started up or in the warm-up process, the scanner 100 first of all scans a calibration sheet, and then uses the image data of the calibration sheet as a reference for the shading correction and compensation of the system and improving the color cast problem of the image. Referring to both FIG. 1A and FIG. 1B, a relative position between a top chassis and a calibration sheet is shown. According to a conventional scanning method, the calibration sheet 108 is fixed in the body 101. Since the calibration sheet 108 is fixed, the top chassis 105 is fixed as well. During the calibrating process, the top chassis 105 keeps scanning the same scan line on the calibration sheet 108. This is called “static calibration”. As shown in FIG. 1B, the top chassis 105 can only scan the scan line positioned at Ax. As for other scan lines, the scan lines corresponding to the positions of A0, A1 to An on the calibration sheet 108 will never be scanned. However, such method has a disadvantage. When the position of Ax on calibration sheet 108 is smudged by dirt or dust, the calibration sheet 108 will be incapable of providing precise reference. As a result, the scanning quality of the scanner 100 is greatly affected.